The present invention generally relates to a maintenance station of an ink jet printer and, more particularly, to a capping and wiping system within the maintenance station which is connected to a common vacuum source for more efficient performance.
An ink jet printer of the so-called "drop-on-demand" type has at least one printhead from which droplets of ink are directed towards a recording medium. Within the printhead, the ink may be contained in a plurality of channels and energy pulses are used to cause the droplets of ink to be expelled, as required, from orifices at the ends of the channels.
In a thermal ink jet printer, the energy pulses are usually produced by resistors, each located in a respective one of the channels, which are individually addressable by current pulses to heat and vaporize ink in the channels. As a vapor bubble grows in any one of the channels, ink bulges from the channel orifice or nozzle until the current pulse has ceased and the bubble begins to collapse. At that stage, the ink within the channel retracts and separates from the bulging ink which forms a droplet moving in a direction away from the channel and towards a recording medium. The channel is then refilled by capillary action, drawing ink from a supply container. Operation of thermal ink jet printers are described, for example, U.S. Pat. Nos. 4,849,774 and 4,571,599.
One particular form of thermal ink jet printer is described in U.S. Pat. No. 4,638,337. That printer is of the carriage type and has a plurality of printheads, each with its own ink supply cartridge, mounted on a reciprocating carriage. The channel orifices in each printhead are aligned perpendicular to the line of movement of the carriage and a swath of information is printed on the stationary recording medium as the carriage is moved in one direction. The recording medium is then stepped, perpendicular to the line of carriage movement, by a distance equal to the width of the printed swath and the carriage is then moved in the reverse direction to print another swath of information.
It has been recognized that there is a need to maintain the ink ejecting orifices of an ink jet printer, for example, by periodically cleaning the orifices when the printer is in use, and/or by capping the printhead when the printer is out of use or is idle for extended periods. The capping of the printhead is intended to prevent the ink in the printhead from drying out. There is also a need to prime a printhead before use, to ensure that the printhead channels are completely filled with ink and contain no contaminants or air bubbles. Maintenance and/or priming stations for the printheads of various types of ink jet printers are described in, for example, U.S. Pat. Nos. 4,855,764, 4,863,717 and 4,746,938 while the removal of gas from the ink reservoir of a printhead during printing is described in U.S. Pat. No. 4,679,059. All of these patents are hereby incorporated by reference.
A continuing problem with prior art capping mechanisms is that of positive pressure buildup when the printhead is in a capped condition. In a typical capping operation, a cap comprised of a ribbed membrane is brought into engagement with the nozzle face of the printhead to seal the nozzle face while at the same instant, the nozzles eject a small amount of ink to increase the humidity in the environment of the cap. This prevents evaporation of the meniscus in the nozzles during the period of time that the printhead is in the capped condition.
For some systems, a dysfunctional effect of this humidification is a positive pressure buildup due to vapor pressure build up in the 70-100 mm Hg range. Temperature differentials may also results in positive pressure buildups in the cap of the same magnitude. With positive pressures of this magnitude, the capillary forces of the menisci in the nozzles are overcome and air is forced into the interior of the nozzles which may contribute to first print out problems. In extreme situations, the printhead ceases printing until an intervention in the form of priming or other recovery methods are used by the customer. The cap must be vented in some manner to rid these deleterious positive pressure buildups; typical solutions are to install valves to periodically release pressure or to reapply the cap sealing pressure on a periodic time schedule.
An associated problem is to maintain the capped printhead nozzle face in a relatively humid environment.